Electrolytic capacitors are often formed from valve action materials that are capable of being oxidized to form a dielectric layer. Typical valve action metals are niobium and tantalum. More recently, capacitors have been developed that employ an anode made from an electrically conductive oxide of niobium and a niobium pentoxide dielectric. Niobium oxide based capacitors have significant advantages over tantalum capacitors. For example, niobium oxide is more widely available and potentially less expensive to process than tantalum. Niobium oxide capacitors are also more stable against further oxidation and thus less prone to thermal runaway when over-voltaged (or otherwise over-loaded) than tantalum and niobium. Further, niobium oxide has several orders of magnitude higher minimum ignition energy compared to niobium and tantalum. Niobium oxide capacitors may also have a unique high resistance failure mechanism that limits the leakage current to a level below the capacitor's thermal runaway point. The dielectric layer of these capacitors is mostly prepared by valve metal or NbO oxidation. The anodic oxidation at appropriate voltage has made valve metals oxides and may be performed by water electrolysis with oxygen generation. However, problems often arise due to the hydrophobicity of the oxides on the anode surface, which tend to repel water and create clusters. This may give rise to anodically grown dielectric films having an inhomogeneous and rough surface, which can lead to leakage current instability at accelerated temperature and voltage load.
As such, a need currently exists for an electrolytic capacitor anode having a reduced number of defects in the dielectric layer.